Method for marking metal blocks and the marked articles

ABSTRACT

Metal blocks to be subjected to heat treatment are marked for identification with a marking composition resistant to the heat treatment conditions so that the marking is not destroyed during the heat treatment. The marking compositions are characterized by the presence as pigment of strontium chromate, magnesium oxide, or mixtures thereof.

United States Patent [191 Dijkstra [111 3,790,398 Feb. 5, 1974 METHOD FOR MARKING'METAL BLOCKS AND THE MARKED ARTICLES [75] Inventor: Waling Dijkstra, Leeuwarden,

Netherlands [73] Assignee: Zandleven Curacao N.V., Curacao,

Netherlands [22] Filed: Jan. 14, 1971 [21] Appl. No.: 106,592

Related U.S. Application Data [63] Continuation of Ser. No. 775,221, Sept. 10, 1968,

abandoned, which is a continuation of Ser. No. 523,551, Jan. 28, 1966, abandoned.

[30] Foreign Application Priority Data Apr. 17, 1965 Germany 47059 [52] U.S. Cl 117/37 R, 117/38, 117/62, 117/127, 117/169 R, l48/31.5, 148/128 [51] Int. Cl. C23c 41/00, C23c 39/00 [58] Field of Search... 106/19, 20; 117/37, 38, 127, ll7/l69 R, 62; 148/31.5, 128

[56] References Cited UNITED STATES PATENTS 2,141,965 12/1938 Aronberg 106/19 OTHER PUBLICATIONS Alexander et al., Anticorrosive Primer, in Industrial & Engineering Chemistry, Oct; 1952, Pg. 2409-2412. Buros et al., Protective Coating For Metals, Rheinhold Publishing, NY. (1939) Pg. 306-307.

Primary Examiner-Alfred L. Leavitt Assistant Examiner-M. F. Esposito 'The marking compositions are characterized by the presence as pigment of strontium chromate, magnesium oxide, or mixtures thereof.

24 Claims, No Drawings METHOD FOR MARKING METAL BLOCKS AND THE MARKED ARTICLES This application is a continuation of application Ser. No. 775,221 FlLED Sept. 10, 1968 now abandoned, which in turn is a continuation of application Ser. No. 523,551, filed Jan. 28, 1966 now abandoned.

Thepresent invention relates to a material suitable for marking glowing metal articles heated to high temperatures, for example up to 1,600C. so that the marks are visible when these metal articles are in the glowing state.

The problem of marking a hot metal is encountered in the technology of steel production when the crude metal for example in square or rectangular blocks, 1

from which sheet steel or wires are to be obtained by subsequent rolling processes, isbrought to the annealing temperature, for example about 1,200C. in a furmice. In continuous batch production in a large roll mill it is desirable to mark each block permanently with a code sign, in order to be able to recognize it immediately and unambiguously when transferring it to the rollers at white heat. This is important for the foreman in order to be able to set the appropriate rolling conditions. it is not possible to rely on the metal blocks charged into the oven being removed therefrom in the same sequence, and in practice some displacements always take place. It is necessary to know the nature of the particular metal immediately prior to the rolling process.

Attempts have been made for a long time to mark the individual metal blocks for heating to annealing temperatures. The problemis to develop a marking ink which is not only able to survive the temperatures of the annealing process and also to maintain contact with the glowing metal, but which must furthermore contrast with the metal in the glowing state, since it is particularly at white heat that the marking should bevisible. In practice it has not hitherto been possible to develop such an effective marking material. Certain carbides are used, but these only give very weak contrast marks in the glowing state,'and this does not permit reliable individual marking. lnste'ad, one rather depends on marking individual blocks at l certain intervals throughout a batch, in order to be able to telI when one is working withina certain range of fed-in raw metal blocks.

Pigments have now been found which are suited to, on the one hand, survive the fierce conditions during annealing, and on the other hand to provide the desired clearly visible cont'rastmarks. The three pigments suitable for this are: chromium (lll) oxide, magnesium oxide and, especially, strontium chromate. Of these the applied number glows bright through the dark oxide layer and can be discerned without difficulty. If this crude block is then allowed to pass through the rolmium oxide and magnesium oxide admittently also produce writing which is visible immediately after the crude block has left the furnace, and here again in the form'of brighter writing. However, after once rolling these crude blocks the writing in chromium oxide and magnesium oxide can no longer be discerned, or only be discerned with difficulty. Nevertheless, these pigments also have some technological importance since the foreman can clearly recognize, at the beginning of the rolling process, with which particular crude metal block he is dealing. He can make an appropriate note and can then immediately mark this piece of metal after cooling. Thus with these two pigments one again overcomes the greatest difficulty, namely the reliable identification of the individual metal piece after heating up to annealing temperatures in the furnace.

The pigments are appropriately used -in the form of an aqueous suspension, for' practical purposes in the form of i a thick aqueous paste which is preferably brought to a suitable consistency by using binders, particularly of an organic type. The binders may be linseed or soja oil and composition may also contain quartz flour and small amounts of turpentine, mica, silicone oil, silicon carbide and/or a drying agent. The marking compositions can contain up to 10 percent by weight, based on the total weight of the composition, of turpentine, mica, silicone "oil or silicon carbide. The nature of the binder is not decisive, since it burns away during the annealing process, andis only of some significance with regard to the easier application of the marking ink before annealing. t

For marking compositions wherein the pigment is strontium chromate, said pigment'may constitute from 1.0 to 70 percent of the composition. -Also where the pigment is strontium chromate, the composition can comprise from to 100 percent, by weight of the strontium chromate, of linseed oil, soja oil or a mixture thereof.

On the basis of experience to date the pigments survive high temperatures. in the range of l,200 to 1,500C. for many hours. For this, experiments were carried out with annealing times of 4 to 16 hours, i.e.,

times which are entirely adequate for industrial usage.

The use of the new marking material is not restricted to the production of steel. it may be used with equal effectiveness for other metals heated to high temperatures, for example lead, zinc, aluminium, brass or copper. The following Examples illustrate the invention.

EXAMPLE 1 A paste with which'crude'metal blocks are marked is prepared from parts by weight of strontium chromate and 60 to 100 parts by weight of a mixture of linseed oil and soja oil. The crude metal blocks marked in this way are then heated to l,200C. The writing is very well visible on leaving the furnace. It is still visible even after rolling 5 times. i

EXAMPLE 2 A mixture of 100 parts by weight of strontium chromate, parts by weight of magnesium oxide, 60 parts by weight of linseed oil and soja oil together with small amounts of turpentine, mica, quartz flour, silicone oil and a drier are produced. The marks applied to crude metal blocks by means of this can still be clearly recognized even after several hours annealing at white heat and subsequent multiple rolling.

EXAMPLE 3 Various metals were marked with a marking ink according to the invention, having the following composition:

Linseed oil 36.0% Silicone oil 2.5% Magnesium oxide 4.5% Strontium chromate 50.0% Green chromium oxide 4.0% Silicon carbide 2.0% Mica 1.0%

and were then heated to temperatures just below their melting point. The following results were obtained;

Metal Temperature Assessment of visibility of the mark.

Lead 250C Clearly visible as a yellowish-green sign Zinc 350C Clearly visible as a yellow sign. Aluminium 600C Clearly visible as a yellowish-green sign Brass 800C Visible as a somewhat darker sign against a light background. Copper [000C Visible as a less dark sign against a light background.

ture thereof.

3. A method according to claim 1 wherein said pigment constitutes from 10 to 70 percent of the composition.

4. Method according to claim 1, wherein in said heating said article is heated to a glowing state.

5.,Method' according to claim 1, said heating comprising annealing of the article.

6. Method according to claim 1, and the step of rolling the article after said heat treatment, the marking integrity being retained throughout said rolling.

7. Method according to claim 1, said metal being steel.

8. Method according to claim 7, said heating comprising annealing of the article.

9. Method according to claim 7, said heating comprising heating at above about l,200C.

10. Method according to claim 7, said heating being in the range of about l,200-l,600C.

11. Method according to claim 7, an oxide layer forming on the article during said heat treatment, and the step of rolling the article after said heat treatment, the marking integrity being retained 12. Method according to claim 11, said heating comprising heating at above about l,200C.

13. Method according to claim 1, an oxide layer forming on the article during said heat treatment, the marking being discernible through the oxide layer.

14. Method according to claim 13, said metal being steel. 1

15. Method according to claim 14, said heating comprising heatingto above l,200C.

16. Method according to claim 14, said heating comprising heating to above l,200C for 4 to 16 hours.

17. Method according to claim 13, the marking integrity being retained after removal of the oxide layer from the article.

18. Method according to claim l4, the marking integrity being retained after removal of the oxide layer from the article.

19. Method according to claim 15, the marking integ- I rity being retained after removal of the oxide layer from the article.

20. Method according to claim 16, the marking integrity being retained after removal of the oxide layer from the article.

21. Metal article at elevated, metal working or treating temperature bearing identification marking consisting essentially of pigment strontium chror'nate bonded to the metal and forming the identifying characters.

22. Metal article according to claim 21, in the glowing state. r

23. Metal article according to claim 21, at about l,200 1,600C.

24. Metal article having on the surface thereof identification marking provided by marking composition for identifying metal articles and retaining marking integrity throughout heating of the article to a glowing state comprising pigment strontium chromate and a binder therefor, the binder decomposing wherrthe marked metal shape is heated to the glowing state leaving the marking visible in the glowing state.

t i I 

2. A method according to claim 1, wherein said composition comprises from 60 to 100 percent by weight of the strontium chromate, of linseed oil, soja oil or a mixture thereof.
 3. A method according to claim 1 wherein said pigment constitutes from 10 to 70 percent of the composition.
 4. Method according to claim 1, wherein in said heating said article is heated to a glowing state.
 5. Method according to claim 1, said heating comprising annealing of the article.
 6. Method according to claim 1, and the step of rolling the article after said heat treatment, the marking integrity being retained throughout said rolling.
 7. Method according to claim 1, said metal being steel.
 8. Method according to claim 7, said heating comprising annealing of the article.
 9. Method according to claim 7, said heating comprising heating at above about 1,200*C.
 10. Method according to claim 7, said heating being in the range of about 1,200*-1,600*C.
 11. Method according to claim 7, an oxide layer forming on the article during said heat treatment, and the step of rolling the article after said heat treatment, the marking integrity being retained
 12. Method according to claim 11, said heating comprising heating at above about 1,200*C.
 13. Method according to claim 1, an oxide layer forming on the article during said heat treatment, the marking being discernible through the oxide layer.
 14. Method according to claim 13, said metal being steel.
 15. Method according to claim 14, said heating comprising heating to above 1,200*C.
 16. Method according to claim 14, said heating comprising heating to above 1,200*C for 4 to 16 hours.
 17. Method according to claim 13, the marking integrity being retained after removal of the oxide layer from the article.
 18. Method according to claim 14, the marking integrity being retained after removal of the oxide layer from the article.
 19. Method according to claim 15, the marking integrity being retained after removal of the oxide layer from the article.
 20. Method according to claim 16, the marking integrity being retained after removal of the oxide layer from the article.
 21. Metal article at elevated, metal working or treating temperature bearing identification marking consisting essentially of pigment strontium chromate bonded to the metal and forming the ideNtifying characters.
 22. Metal article according to claim 21, in the glowing state.
 23. Metal article according to claim 21, at about 1,200* - 1, 600*C.
 24. Metal article having on the surface thereof identification marking provided by marking composition for identifying metal articles and retaining marking integrity throughout heating of the article to a glowing state comprising pigment strontium chromate and a binder therefor, the binder decomposing when the marked metal shape is heated to the glowing state leaving the marking visible in the glowing state. 